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Genetics Research Update – Dr. Danielle M. Andrade

Small variations in DNA (the genetic material that contains a blueprint for our development) are natural and are what makes each person’s DNA code unique. However, when variation causes certain sections of DNA to disappear, it can lead to disease. This is the case with 22q11.2 deletion syndrome, or 22q11.2 DS (the name may sound complicated, but it really just pinpoints the location of the missing DNA). Humans have 23 pairs of chromosomes, and a single chromosome can contain thousands of genes, which are sequences of DNA. To understand this relationship, think of our entire DNA code as a textbook. The book chapters represent chromosomes, and the sentences in each chapter represent our genes. The missing DNA in 22q11.2 DS contains 46 genes (genes code for proteins, the building blocks of our body).

This syndrome affects one in 4,000 people and has been linked with damage to tissues and organs, such as the heart, ears, and brain. People with this syndrome are at risk of intellectual disabilities, seizures and psychiatric illnesses such as schizophrenia. Although children with 22q11.2 DS have been well-studied, Dr. Danielle Andrade and her colleagues wanted to know if this deletion was also linked to epilepsy or an increased risk of seizures in adults with 22q11.2 DS.

Dr. Andrade and her team reviewed the medical records of 202 adults (aged 18-63) with 22q11.2 DS. They found that 32 of these patients had at least one seizure. Twenty-three of the 32 patients had acute symptomatic seizures. This means that the seizures only happened when patients had low calcium levels or started taking an antipsychotic drug (antipsychotics are used to treat patients who may have delusions, hallucinations or paranoia). The other 9 of the 32 patients met the criteria for the diagnosis of epilepsy, meaning they had recurring, unprovoked seizures that were not associated with any triggering factors. These rates of acute symptomatic seizures and epilepsy in patients with 22q11.2 DS are much higher than the general population. These data suggest that the deletion is not only linked to higher rates of epilepsy, but also to a higher chance of seizure activity in people without epilepsy.

It is not clear how having 22q11.2 DS leads to seizures. One possibility is that the low calcium levels caused by this syndrome change the way the brain communicates using electrical signals, which may induce seizures. 22q11.2 DS may also cause changes in the brain’s structure, resulting in brain regions that do not develop normally and are prone to seizures. Finally, the deletion may create an imbalance in the amount of proteins produced by those genes, affecting not only the electrical signals in the brain, but also how the brain responds to antipsychotic medication.

In summary, this study found that adults with 22q11.2 DS have an increased risk of having both epilepsy and non-recurrent seizures, especially triggered by antipsychotic medication. The risk of having acute symptomatic seizures was higher than the risk of developing epilepsy in adults. Health care providers should be aware of this increased risk in patients with this syndrome, especially if the patients need antipsychotic drugs.